A thorough understanding of genetic factors (both host and viral) effecting the pathogenic and transmission consequences of host-HIV-1 interactions is essential to all aspects of public health from diagnostic, transmission, and prevention strategies. Specific aim: The potential role played by HLA-G allele in vertical transmission will be examined. Aims: i) Screen and identify and characterize genetic variations in the HLA-G DNA samples from HIV-1-infected and uninfected mother/child pairs and compare HLA-G percentage variability among samples. ii) Evaluate for potential correlation(s) between HLA-G allele sequence variant frequencies in exons 2-7 and relationships to vertical transmission among the mother/child pairs. Approach: DNA samples of HIV-1-infected and uninfected mother/child pairs will be obtained from CDC (PACTS- study). RAPD-PCR, allele-specific PCR, SSCP-PCR will be employed in this study, followed by DNA cloning/sequencing. All distinct PCR bands will be excised and cloned. Approximately 5-10 clones per PCR product will be sequenced. PASA method will be used to confirm any mutation that may exist. Fisher's exact test (x2), logistic regression will be utilized to compared the groups value. Maximum likelihood, Hardy-Weinberg equilibrium, and linkage disequilibrium parameter analyses will be used to check for random distribution of any mutation of HLA-G at each locus among the samples, and the risk association of HLA-G variation(s) on the frequency of HIV-1 vertical transmission.